Electrostatic chucking method and substrate processing apparatus

ABSTRACT

An electrostatic chucking method uses a substrate processing apparatus including an electrostatic chuck, a focus ring, a supply unit configured to supply a heat transfer medium to a space formed between the focus ring and the electrostatic chuck, and a plurality of electrodes provided at a region in the electrostatic chuck which corresponds to the focus ring. The electrostatic chucking method includes supplying by the supply unit the heat transfer medium to the space for a plasma processing period for which a plasma for processing the substrate is generated, and applying different voltages to the plurality of electrodes to attract and hold the focus ring on the electrostatic chuck for a period other than the plasma processing period.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/975,377, filed Dec. 18, 2015 which claims priority to Japanese PatentApplication No. 2014-262170 filed on Dec. 25, 2014, the disclosures ofwhich are incorporated herein in their entirety by reference, andpriority is claimed to each of the foregoing.

FIELD OF THE INVENTION

The disclosure relates to an electrostatic chucking method and asubstrate processing apparatus.

BACKGROUND OF THE INVENTION

In a conventional substrate processing apparatus, when a substrate issubjected to a plasma processing, the substrate is attracted and held onan electrostatic chuck by an electrostatic force. A focus ring isprovided on the electrostatic chuck to surround a region where thesubstrate is mounted.

In the above substrate processing apparatus, when a plasma used for theplasma processing for the substrate is generated, a temperature of thefocus ring is increased by the plasma. To that end, a heat transfermedium is supplied to a space formed between the focus ring and theelectrostatic chuck to suppress the temperature increase. By supplyingthe heat transfer medium to the space formed between the focus ring andthe electrostatic chuck, heat of the focus ring is transferred to theelectrostatic chuck via the heat transfer medium.

If airtightness of the space formed between the focus ring and theelectrostatic chuck is not ensured, the heat transfer medium supplied tothe space leaks to the outside, which results in deterioration of theheat transfer between the focus ring and the electrostatic chuck.Therefore, it is preferable to ensure the airtightness between the focusring and the electrostatic chuck.

Therefore, there is suggested a technique of attracting and holding afocus ring on an electrostatic chuck by applying a voltage to anelectrode provided at a region in the electrostatic chuck whichcorresponds to the focus ring, see, e.g. Japanese Patent No. 4913313.

However, such a conventional technique has a problem that the amount ofleakage of the heat transfer medium supplied to the space formed betweenthe focus ring and the electrostatic chuck may increase.

In other words, in the above conventional technique, misalignmentbetween the focus ring and the electrostatic chuck may occur because thefocus ring is not attracted and held on the electrostatic chuck in aperiod other than a plasma processing period in which a plasma forprocessing the substrate is generated. If misalignment between the focusring and the electrostatic chuck occurs, the airtightness of the spaceformed between the focus ring and the electrostatic chuck deteriorates,and thus, the heat transfer medium supplied to the space leaks to theoutside. As a result, in the above conventional technique, the amount ofleakage of the heat transfer medium supplied to the space formed betweenthe focus ring and the electrostatic chuck may increase.

SUMMARY OF THE INVENTION

In accordance with an aspect, there is provided an electrostaticchucking method using a substrate processing apparatus including anelectrostatic chuck, a focus ring, a supply unit configured to supply aheat transfer medium to a space formed between the focus ring and theelectrostatic chuck, and a plurality of electrodes provided at a regionin the electrostatic chuck which corresponds to the focus ring. Theelectrostatic chucking method includes supplying by the supply unit theheat transfer medium to the space for a plasma processing period forwhich a plasma for processing the substrate is generated, and applyingdifferent voltages to the plurality of electrodes to attract and holdthe focus ring on the electrostatic chuck for a period other than theplasma processing period.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the disclosure will become apparent from thefollowing description of embodiments, given in conjunction with theaccompanying drawings, in which:

FIG. 1 is a cross sectional view showing a schematic configuration of aplasma processing apparatus according to a first embodiment;

FIG. 2 shows an example of an installation of an electrode plate;

FIG. 3 shows an example of a timechart of an electrostatic attractionprocess of the first embodiment;

FIG. 4 shows an example of a result of an experiment for comparing theamount of leakage of a heat transfer gas supplied to a space formedbetween an electrostatic chuck and a focus ring in the first embodiment;

FIG. 5 shows an example of a timechart of an electrostatic attractionprocess of a second embodiment;

FIGS. 6A and 6B show examples of results of experiments of comparing theamount of leakage of a heat transfer gas supplied to the space formedbetween the electrostatic chuck and the focus ring in the secondembodiment;

FIG. 7 explains a first arrangement example of a plurality ofelectrodes;

FIGS. 8A and 8B explain a second arrangement example of the plurality ofelectrodes; and

FIG. 9 explains a third arrangement example of the plurality ofelectrodes.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, various embodiments will be described in detail withreference to the accompanying drawings. Like reference numerals refer tolike or corresponding parts throughout the drawings.

First Embodiment

FIG. 1 is a cross sectional view showing a schematic configuration of aplasma processing apparatus according to a first embodiment. In thepresent embodiment, a substrate processing apparatus is configured as anRIE (Reactive Ion Etching) type plasma processing apparatus. However,the substrate processing apparatus may be applied to a plasma etchingapparatus or a plasma CVD apparatus which uses a surface wave plasma.

Referring to FIG. 1, the plasma processing apparatus configured as anRIE type plasma processing apparatus includes a cylindrical processingchamber 10 made of a metal, e.g., aluminum or stainless steel, which isframe grounded. Provided in the processing chamber 10 is a circularplate-shaped susceptor (lower electrode) 11 for mounting thereon a waferW as a processing target (substrate). The susceptor is made of, e.g.,aluminum, and supported, through a cylindrical insulating supportingmember 12, by a cylindrical supporting part 13 extending verticallyupward from a bottom portion of the processing chamber 10.

A gas exhaust path 14 is formed between a sidewall of the processingchamber 10 and the cylindrical supporting part 13. An annular baffleplate 15 is provided at an inlet of the gas exhaust path 14 or in thegas exhaust path 14. A gas exhaust port 16 is provided at a bottomportion of the processing chamber 10. A gas exhaust unit 18 is connectedto the gas exhaust port 16 through a gas exhaust line 17. The gasexhaust unit 18 has a vacuum pump and decreases a pressure in aprocessing space in the processing chamber 10 to a predetermined vacuumlevel. The gas exhaust line 17 has an automatic pressure control valve(hereinafter, referred to as “APC valve”) (not shown) that is anadjustable butterfly valve. The APC valve automatically controls thepressure in the processing chamber 10. A gate valve 20 foropening/closing a loading/unloading port 19 for a wafer W is installedon the sidewall of the processing chamber 10.

A high frequency power supply 21 for plasma generation and RIE iselectrically connected to the susceptor 11 via a matching unit 22 and apower feed rod 23. The high frequency power supply 21 applies a highfrequency power having a predetermined high frequency, e.g., 60 MHz, tothe susceptor 11. A shower head 24 serving as an upper electrode of aground potential which will be described later is provided at a ceilingportion of the processing chamber 10. Accordingly, a high frequencyvoltage from the high frequency power supply 21 is applied between thesusceptor 11 and the shower head 24.

An electrostatic chuck 25 for attracting and holding the wafer W by anelectrostatic attractive force is provided on a top surface of thesusceptor 11. The electrostatic chuck 25 includes: a circularplate-shaped central portion 25 a on which the wafer W is mounted; andan annular outer peripheral portion 25 b. The central portion 25 aprotrudes upward in the drawing with respect to the outer peripheralportion 25 b. A focus ring 30 is provided on a top surface of the outerperipheral portion 25 b to surround the central portion 25 a. Thecentral portion 25 a is formed by sandwiching an electrode plate 25 cmade of a conductive film between a pair of dielectric films. The outerperipheral portion 25 b is formed by sandwiching an electrode plate 25 dmade of a conductive film between a pair of dielectric films. A DC powersource 26 is electrically connected to the electrode plate 25 c via aswitch 27. DC power supplies 28-1 and 28-2 are electrically connected tothe electrode plate 25 d via respective switches 29-1 and 29-2. Theelectrostatic chuck 25 attracts and holds the wafer W on theelectrostatic chuck 25 by an electrostatic force such as a Coulomb forceor the like which is generated by the DC voltage applied from the DCpower supply 26 to the electrode plate 25 c. Further, the electrostaticchuck 25 attracts and holds the focus ring 30 on the electrostatic chuck25 by an electrostatic force such as a Coulomb force, which is generatedby the voltage applied from the DC power supplies 28-1 and 28-2 to theelectrode plate 25 d. The installation of the electrode plate 25 d willbe described in detail later.

Provided in the susceptor 11 is an annular coolant path 31 extending,e.g., in a circumferential direction. A coolant, e.g., cooling water, ofa predetermined temperature is supplied into the coolant path 31 from achiller unit 32 through lines 33 and 34 to be circulated. A processingtemperature of the wafer W on the electrostatic chuck 25 is controlledby the temperature of the coolant.

A heat transfer gas supply unit 35 is connected to the electrostaticchuck 25 through a gas supply line 36. The gas supply line 36 isbranched into a wafer side line 36 a extending to the central portion 25a of the electrostatic chuck 25 and a focus ring side line 36 bextending to the outer peripheral portion 25 b of the electrostaticchuck 25. The heat transfer gas supply unit 35 supplies a heat transfergas to a space formed between the central portion 25 a of theelectrostatic chuck 25 and the wafer W through the wafer side line 36 a.Further, the heat transfer gas supply unit 35 supplies a heat transfergas to a space formed between the outer peripheral portion 25 b of theelectrostatic chuck 25 and the focus ring 30 through the focus ring sideline 36 b. A thermally conductive gas, e.g., He gas, is suitable for theheat transfer gas. The heat transfer gas is an example of the heattransfer medium. The heat transfer gas supply unit 35 is an example ofthe supply unit for supplying a heat transfer medium.

The shower head 24 provided at the ceiling portion includes: anelectrode plate 37 as a bottom surface having a plurality of gasventholes 37 a; and an electrode holder 38 for detachably holding theelectrode plate 37. A buffer space 39 is provided inside the electrodeholder 38. A gas supply line 41 from a processing gas supply unit 40 isconnected to a gas inlet 38 a of the buffer space 39. A magnet 42extending annularly or concentrically is provided around the processingchamber 10.

The components of the plasma processing apparatus, e.g., the gas exhaustunit 18, the high frequency power supply 21, the switches 27, 29-1 and29-2 for the electrostatic chuck, the DC power supplies 26, 28-1 and28-2, the chiller unit 32, the heat transfer gas supply unit 35, theprocessing gas supply unit 40 and the like, are connected to a controlunit 43. The control unit 43 controls the respective components of theplasma processing apparatus.

The control unit 43 includes a central processing unit (CPU) (not shown)and a storage unit such as a memory or the like. By reading out andexecuting a program and a processing recipe stored in the storage unit,a desired process is performed in the plasma processing apparatus. Forexample, the control unit 43 performs an electrostatic attractionprocess for electrostatically attracting and holding the focus ring 30.The electrostatic attraction process performed by the control unit 43will be described later in detail.

In the processing chamber 10 of the plasma processing apparatus, ahorizontal magnetic field oriented in one direction is generated by themagnet 42 and, also, a vertical RF electric field is generated by thehigh frequency voltage applied between the susceptor 11 and the showerhead 24. Accordingly, magnetron discharge occurs via the processing gasin the processing chamber 10. As a result, a high-density plasma isgenerated from the processing gas near the surface of the susceptor 11.

In this plasma processing apparatus, in order to perform a dry etchingprocess, the gate valve 20 is opened, and a wafer W as a processingtarget is loaded into the processing chamber 10 and mounted on theelectrostatic chuck 25. Then, a processing gas (e.g. a gaseous mixtureof C₄F₈ gas, O₂ gas and Ar gas which are mixed at a predetermined flowrate ratio) is introduced at a predetermined flow rate and flow rateratio from the processing gas supply unit 40 into the processing chamber10. The pressure in the processing chamber 10 is set to a predeterminedvalue by the gas exhaust unit 18 and the like. A high frequency power issupplied to the susceptor 11 from the high frequency power supply 21. ADC voltage is applied to the electrode plate 25 c of the electrostaticchuck 25 from the DC power supply 26. Accordingly, wafer W is attractedand held on the electrostatic chuck 25. The processing gas injected fromthe shower head 24 is turned into a plasma as described above, and asurface of the wafer W is etched by radicals or ions generated by theplasma.

In this plasma processing apparatus, the processing gas is dissociatedinto a desirable dissociation state by applying a high frequency powerin a frequency range (50 MHz or above) much higher than a conventionalfrequency level (generally 27 MHz or less) to the susceptor 11. As thedissociated processing gas becomes a plasma, a high-density plasma canbe generated even under a low pressure condition. Such high-densityplasma enables an oxidation process and a nitriding process to becarried out with a low damage, and greatly contributes to highperformance and low power consumption of semiconductor devices. In otherwords, it is possible to prevent breakage and contamination of the waferW which would be caused by high-energy particles in the plasma or metalatoms emitted from inner walls of the processing chamber due to acollision of the high-energy particles. Therefore, the plasma can beapplied to a gate formation step which requires formation of ahigh-quality insulation film. Accordingly, the plasma processingapparatus of the present embodiment can deal with technical problemscaused by the progress of microprocessing of the wafer W.

Next, the installation of the electrode plate 25 d shown in FIG. 1 willbe described. FIG. 2 shows an example of the installation of theelectrode plate 25 d. As shown in FIG. 2, the electrode plate 25 d isprovided at a region in the outer peripheral portion 25 b of theelectrostatic chuck 25 which corresponds to the focus ring 30. Theelectrode plate 25 d includes an inner peripheral electrode plate 25 d-1and an outer peripheral electrode plate 25 d-2.

The inner peripheral electrode plate 25 d-1 is disposed in an annularshape at the inner peripheral side of the focus ring 30. The innerperipheral electrode plate 25 d-1 is electrically connected to the DCpower supply 28-1 via the switch 29-1. A positive or a negative voltagefor attracting and holding the focus ring 30 on the electrostatic chuck25 is selectively applied to the inner peripheral electrode plate 25 d-1from the DC power supply 28-1. The polarity of the voltage applied fromthe DC power supply 28-1 to the inner peripheral electrode plate 25 d-1is switched by the control unit 43.

The outer peripheral electrode plate 25 d-2 is disposed in an annularshape at the outer peripheral side of the focus ring 30. The outerperipheral electrode plate 25 d-2 is electrically connected to the DCpower supply 28-2 via the switch 29-2. A positive or a negative voltagefor attracting and holding the focus ring 30 on the electrostatic chuck25 is selectively applied to the outer peripheral electrode plate 25 d-2from the DC power supply 28-2. The polarity of the voltage applied fromthe DC power supply 28-2 to the outer peripheral electrode plate 25 d-2is switched by the control unit 43.

Next, the electrostatic attraction process performed by the control unit43 of the first embodiment will be described. FIG. 3 shows an example ofa timechart of the electrostatic attraction process of the firstembodiment.

Referring to FIG. 3, “WAF-HV(V)” represents a timechart showing changesin the voltage for attracting and holding the wafer W on the centralportion 25 a of the electrostatic chuck 25 which is applied to theelectrode plate 25 c; “FR-A-HV(V)” represents a timechart showingchanges in the voltage for attracting and holding the focus ring 30 onthe outer peripheral portion 25 b of the electrostatic chuck 25 which isapplied to the inner peripheral electrode plate 25 d-1; “FR-B-HV(V)”represents a timechart showing changes in the voltage for attracting andholding the focus ring 30 on the outer peripheral portion 25 b of theelectrostatic chuck 25 which is applied to the outer peripheralelectrode plate 25 d-2; and “He supply” represents a timechart showingchanges of the supply state of He gas supplied as a heat transfer gasfrom the heat transfer gas supply unit 35 to the space formed betweenthe electrostatic chuck 25 and the focus ring 30.

Referring to FIG. 3, “plasma processing period” represents a period inwhich a plasma for processing the wafer W is generated. “Loading”represents a period in which the wafer W is loaded into the processingchamber 10. “Unloading” represents a period in which the wafer W isunloaded from the processing chamber 10.

In the electrostatic attraction process of the first embodiment, in theplasma processing period, the control unit 43 controls the heat transfergas supply unit 35 to supply a heat transfer gas to the space formedbetween the electrostatic chuck 25 and the focus ring 30. Further, in aperiod other than the plasma processing period, the control unit 43controls such that different voltages are applied to the innerperipheral electrode plate 25 d-1 and the outer peripheral electrodeplate 25 d-2 to generate a potential difference between the innerperipheral electrode plate 25 d-1 and the outer peripheral electrodeplate 25 d-2 in a state where the heat transfer gas is not supplied tothe space formed between the electrostatic chuck 25 and the focus ring30.

In other words, in a period other than the plasma processing period,i.e., a period in which the wafer W is loaded into the processingchamber 10, the control unit 43 controls the heat transfer gas supplyunit 35 not to supply the heat transfer gas to the space formed betweenthe electrostatic chuck 25 and the focus ring 30, as shown in FIG. 3.Further, in the period in which the wafer W is loaded into theprocessing chamber 10, the control unit 43 controls such that differentvoltages are applied to the inner peripheral electrode plate 25 d-1 andthe outer peripheral electrode plate 25 d-2 to generate a potentialdifference between the inner peripheral electrode plate 25 d-1 and theouter peripheral electrode plate 25 d-2 in a state where the heattransfer gas is not supplied to the space formed between theelectrostatic chuck 25 and the focus ring 30. Specifically, the controlunit 43 controls such that a voltage of a predetermined polarity isapplied to the inner peripheral electrode plate 25 d-1 from the DC powersupply 28-1 and a voltage of the opposite polarity is applied to theouter peripheral electrode plate 25 d-2 from the DC power supply 28-2.In the example shown in FIG. 3, the control unit 43 controls such that apositive voltage of 2500V is applied to the inner peripheral electrodeplate 25 d-1 and a negative voltage of −2500V is applied to the outerperipheral electrode plate 25 d-2 to generate a potential differencebetween the inner peripheral electrode plate 25 d-1 and the outerperipheral electrode plate 25 d-2. Accordingly, an electrostatic forceis generated by the potential difference between the inner peripheralelectrode plate 25 d-1 and the outer peripheral electrode plate 25 d-2and the focus ring 30 is attracted and held on the electrostatic chuck25 by the electrostatic force thus generated. As a result, in the periodin which the wafer W is loaded into the processing chamber 10, amisalignment between the electrostatic chuck 25 and the focus ring 30 isavoided and an airtightness of the space formed between theelectrostatic chuck 25 and the focus ring 30 is ensured.

The control unit 43 stops the application of the voltage to theelectrode plate 25 c in the period in which the wafer W is loaded intothe processing chamber 10.

Next, in the plasma processing period, the control unit 43 controls suchthat a positive voltage is applied to the inner peripheral electrodeplate 25 d-1 from the DC power supply 28-1 and a positive voltage isapplied to the outer peripheral electrode plate 25 d-2 from the DC powersupply 28-2. In the example shown in FIG. 3, the control unit 43controls such that a positive voltage of 2500V is applied to the innerperipheral electrode plate 25 d-1 and the outer peripheral electrodeplate 25 d-2 to generate a potential difference between the focus ring30 which is set to a ground potential through the plasma and the innerand the outer peripheral electrode plate 25 d-1 and 25 d-2. Accordingly,an electrostatic force is generated by the potential difference betweenthe inner and the outer peripheral electrode plate 25 d-1 and 25 d-2 andthe focus ring 30 which is set to the ground potential through theplasma, and the focus ring 30 is attracted and held on the electrostaticchuck 25 by the electrostatic force thus generated. Then, in the plasmaprocessing period, the heat transfer gas is supplied from the heattransfer gas supply unit 35 to the space formed between theelectrostatic chuck 25 and the focus ring 30. Since the airtightness ofthe space formed between the electrostatic chuck 25 and the focus ring30 is ensured in the period in which the wafer W is loaded into theprocessing chamber 10, the leakage of the heat transfer gas suppliedfrom the heat transfer gas supply unit 35 is suppressed in the plasmaprocessing period.

In the plasma processing period, the control unit 43 controls such thata voltage is applied to the electrode plate 25 c to generate anelectrostatic force on the electrostatic chuck 25 and allow the wafer Wloaded into the processing chamber 10 to be attracted and held on theelectrostatic chuck 25.

Next, in a period other than the plasma processing period, i.e., aperiod in which the wafer W is unloaded from the processing chamber 10,the control unit 43 controls the heat transfer gas supply unit 35 not tosupply the heat transfer gas to the space formed between theelectrostatic chuck 25 and the focus ring 30. In the period in which thewafer W is unloaded from the processing chamber 10, the control unit 43controls such that different voltages are applied to the innerperipheral electrode plate 25 d-1 and the outer peripheral electrodeplate 25 d-2 to generate a potential difference between the innerperipheral electrode plate 25 d-1 and the outer peripheral electrodeplate 25 d-2 in a state where the heat transfer gas is not supplied tothe space formed between the electrostatic chuck 25 and the focus ring30. Specifically, the control unit 43 controls such that a voltage of apredetermined polarity is applied to the inner peripheral electrodeplate 25 d-1 from the DC power supply 28-1 and a voltage of the oppositepolarity is applied to the outer peripheral electrode plate 25 d-2 fromthe DC power supply 28-2. In the example shown in FIG. 3, the controlunit 43 controls such that a positive voltage of 2500V is applied to theinner peripheral electrode plate 25 d-1 and a negative voltage of −2500Vis applied to the outer peripheral electrode plate 25 d-2 to generate apotential difference between the inner peripheral electrode plate 25 d-1and the outer peripheral electrode plate 25 d-2. Accordingly, anelectrostatic force is generated by the potential difference between theinner peripheral electrode plate 25 d-1 and the outer peripheralelectrode plate 25 d-2 and the focus ring 30 is attracted and held onthe electrostatic chuck 25 by the electrostatic force thus generated. Asa result, in the period in which the wafer W is unloaded from theprocessing chamber 10, the misalignment between the electrostatic chuck25 and the focus ring 30 is avoided and the airtightness of the spaceformed between the electrostatic chuck 25 and the focus ring 30 isensured.

The control unit 43 controls stops the application of the voltage to theelectrode plate 25 c in the period in which the wafer W is unloaded fromthe processing chamber 10.

In the substrate processing apparatus of the first embodiment, in theperiod other than the plasma processing period, different voltages areapplied to the inner peripheral electrode plate 25 d-1 and the outerperipheral electrode plate 25 d-2 such that a potential difference isgenerated between the inner peripheral electrode plate 25 d-1 and theouter peripheral electrode plate 25 d-2 in a state where the heattransfer gas is not supplied to the space formed between theelectrostatic chuck 25 and the focus ring 30. Accordingly, anelectrostatic force is generated by the potential difference between theinner peripheral electrode plate 25 d-1 and the outer peripheralelectrode plate 25 d-2, and the focus ring 30 is attracted and held onthe electrostatic chuck 25 by the electrostatic force thus generated.Therefore, in the period other than the plasma processing period, themisalignment between the electrostatic chuck 25 and the focus ring 30 isavoided and the airtightness of the space formed between theelectrostatic chuck 25 and the focus ring 30 is ensured. As a result, inthe plasma processing period, the increase in the amount of leakage ofthe heat transfer gas supplied to the space formed between the focusring 30 and the electrostatic chuck 25 can be suppressed.

FIG. 4 shows an example of a result of an experiment for comparing theamount of leakage of the heat transfer gas supplied to the space formedbetween the electrostatic chuck 25 and the focus ring 30 in the firstembodiment. In FIG. 4, the vertical axis represents the amount ofleakage (sccm) of He gas supplied as the heat transfer gas to the spaceformed between the electrostatic chuck 25 and the focus ring 30, and thehorizontal axis represents the number of execution of the plasmaprocessing. s. In the experiment shown in FIG. 4, upon completion of thefirst plasma processing in an initial plasma processing period, theloading/unloading of the wafer W is carried out and, then, the secondplasma processing is performed in a next plasma processing period. Thesecond plasma processing and the first plasma processing are carried outunder the same processing condition.

In a comparative example 1 of the experiment shown in FIG. 4, the plasmaprocessing was performed without using the electrostatic attractionprocess for applying different voltages to the inner peripheralelectrode plate 25 d-1 and the outer peripheral electrode plate 25 d-2in a period other than the plasma processing period. In a test example1, the plasma processing was performed by using the electrostaticattraction process for applying different voltages to the innerperipheral electrode plate 25 d-1 and the outer peripheral electrodeplate 25 d-2 in a period other than the plasma processing period.

As shown in FIG. 4, in the comparative example 1, the amount of leakageof He gas in the second plasma processing was increased by about 5 sccmcompared to the amount of leakage of He gas in the first plasmaprocessing.

On the other hand, in the test example 1, the amount of leakage of Hegas in the second plasma processing was increased by about 1 sccmcompared to the amount of leakage of He gas in the first plasmaprocessing. In other words, in the test example 1 using theelectrostatic attraction process for applying different voltages to theinner peripheral electrode plate 25 d-1 and the outer peripheralelectrode plate 25 d-2 in the period other than the plasma processingperiod, the increase in the amount of leakage of the heat transfer gassupplied to the space formed between the focus ring 30 and theelectrostatic chuck 25 was suppressed.

Second Embodiment

In the first embodiment, there has been described the example in whichdifferent voltages are applied to a plurality of electrodes in a periodother than the plasma processing period and the heat transfer gas issupplied to the space formed between the electrostatic chuck 25 and thefocus ring 30 in the plasma processing period. However, the disclosureis not limited thereto. For example, the increase in the amount ofleakage of the heat transfer gas can be suppressed by applying differentvoltages to a plurality of electrodes arranged at predeterminedpositions in a plasma processing period to attract and hold the focusring 30 on the electrostatic chuck 25. Specifically, in a cleaningperiod in which a plasma for cleaning the processing chamber 10 isgenerated, the heat transfer gas is supplied to the space formed betweenthe electrostatic chuck 25 and the focus ring 30. In that case,different voltages may be applied to a plurality of electrodes.Therefore, in the second embodiment, an example in which differentvoltages are applied to a plurality of electrodes in the cleaning periodwill be described. The configuration of the plasma processing apparatusaccording to the second embodiment is the same as that of the plasmaprocessing apparatus according to the first embodiment. Therefore, thedescription thereof will be omitted.

FIG. 5 shows an example of a timechart of the electrostatic attractionprocess of the second embodiment.

Referring to FIG. 5, “WAF-HV(V)” represents a timechart showing changesin the voltage for attracting and holding the wafer W on the centralportion 25 a of the electrostatic chuck 25 which is applied to theelectrode plate 25 c; “FR-A-HV(V)” represents a timechart showingchanges in the voltage for attracting and holding the focus ring 30 onthe outer peripheral portion 25 b of the electrostatic chuck 25 which isapplied to the inner peripheral electrode plate 25 d-1; “FR-B-HV(V)”represents a timechart showing changes in the voltage for attracting andholding the focus ring 30 on the outer peripheral portion 25 b of theelectrostatic chuck 25 which is applied to the outer peripheralelectrode plate 25 d-2; and “He supply” represents a timechart showingchanges of the supply state of He gas supplied as a heat transfer gasfrom the heat transfer gas supply unit 35 to the space formed betweenthe electrostatic chuck 25 and the focus ring 30.

Referring to FIG. 5, “plasma processing period” represents a period inwhich a plasma for processing the wafer W is generated. “Loading”represents a period in which the wafer W is loaded into the processingchamber 10. “Unloading” represents a period in which the wafer W isunloaded from the processing chamber 10. “WLDC” represents a period inwhich a plasma for cleaning the processing chamber 10 is generated(hereinafter, referred to as “cleaning period”) after the wafer W isunloaded from the processing chamber 10 and before a next wafer W isloaded into the processing chamber 10.

The electrostatic attraction process of the second embodiment isbasically the same as that of the first embodiment except the followingfeatures. Therefore, the description of the same electrostaticattraction process will be omitted in the following description.

In other words, the control unit 43 controls the heat transfer gassupply unit 35 to supply the heat transfer gas to the space formedbetween the electrostatic chuck 25 and the focus ring 30 in the cleaningperiod as shown in FIG. 5. Further, in the cleaning period, the controlunit 43 controls such that different voltages are applied to the innerperipheral electrode plate 25 d-1 and the outer peripheral electrodeplate 25 d-2 to generate a potential difference between the innerperipheral electrode plate 25 d-1 and the outer peripheral electrodeplate 25 d-2 in a state where the heat transfer gas is supplied to thespace formed between the electrostatic chuck 25 and the focus ring 30.Specifically, the control unit 43 controls such that a voltage of apredetermined polarity is applied to the inner peripheral electrodeplate 25 d-1 from the DC power supply 28-1 and a voltage of the oppositepolarity is applied to the outer peripheral electrode plate 25 d-2 fromthe DC power supply 28-2. In the example shown in FIG. 5, the controlunit 43 controls such that a positive voltage of 2500V is applied to theinner peripheral electrode plate 25 d-1 and a negative voltage of −2500Vis applied to the outer peripheral electrode plate 25 d-2 to generate apotential difference between the inner peripheral electrode plate 25 d-1and the outer peripheral electrode plate 25 d-2. Accordingly, anelectrostatic force is generated by the potential difference between theinner peripheral electrode plate 25 d-1 and the outer peripheralelectrode plate 25 d-2, and the focus ring 30 is attracted and held onthe electrostatic chuck 25 by the electrostatic force thus generated. Asa result, in the cleaning period, the misalignment between theelectrostatic chuck 25 and the focus ring 30 is avoided, and theairtightness of the space formed between the electrostatic chuck 25 andthe focus ring 30 is ensured.

An electron density of the plasma generated in the cleaning period islower than that of the plasma generated in the plasma processing period.Thus, in the cleaning period, it is difficult to set the focus ring 30to have a ground potential through the plasma. Therefore, if thepotential difference is not generated between the inner peripheralelectrode plate 25 d-1 and the outer peripheral electrode plate 25 d-2,a potential difference is not generated between the focus ring 30 andthe inner and the outer peripheral electrode plate 25 d-1 and 25 d-2.Accordingly, the focus ring 30 may not be attracted and held on theelectrostatic chuck 25.

On the other hand, in the cleaning period the control unit 43 of thepresent embodiment controls such that different voltages are applied tothe inner peripheral electrode plate 25 d-1 and the outer peripheralelectrode plate 25 d-2 to generate a potential difference between theinner peripheral electrode plate 25 d-1 and the outer peripheralelectrode plate 25 d-2. Therefore, even when it is difficult to set thefocus ring 30 to have the ground potential through the plasma in thecleaning period, the focus ring 30 is attracted and held on theelectrostatic chuck 25 by an electrostatic force generated by thepotential difference between the inner peripheral electrode plate 25 d-1and the outer peripheral electrode plate 25 d-2. Accordingly, in thecleaning period, the airtightness of the space formed between theelectrostatic chuck 25 and the focus ring 30 is ensured.

In the substrate processing apparatus according to the secondembodiment, different voltages are applied to the inner peripheralelectrode plate 25 d-1 and the outer peripheral electrode plate 25 d-2such that a potential difference is generated between the innerperipheral electrode plate 25 d-1 and the outer peripheral electrodeplate 25 d-2 in a state where the heat transfer gas is supplied to thespace formed between the electrostatic chuck 25 and the focus ring 30 ina period other than the plasma processing period, i.e., in the cleaningperiod. Accordingly, an electrostatic force is generated by thepotential difference between the inner peripheral electrode plate 25 d-1and the outer peripheral electrode plate 25 d-2 and the focus ring 30 isattracted and held on the electrostatic chuck 25 by the electrostaticforce thus generated. Therefore, in the cleaning period, themisalignment between the electrostatic chuck 25 and the focus ring 30 isavoided, and the airtightness of the space formed between theelectrostatic chuck 25 and the focus ring 30 is ensured. As a result, inthe plasma processing period, the increase in the amount of leakage ofthe heat transfer gas supplied to the space formed between the focusring 30 and the electrostatic chuck 25 can be suppressed.

Although the effect of suppressing the increase in the amount of leakageof the heat transfer gas in a period other than the plasma processingperiod has been described, it is not limited to the cleaning period. Theincrease in the amount of leakage of the heat transfer gas can besuppressed even under a weak plasma processing condition that can be analternative for the cleaning period. For example, in the cleaningperiod, a high frequency power of 800 W is used as a high frequencypower for plasma generation. Accordingly, under the alternative weakplasma processing condition, a plasma is generated by a high frequencypower ranging from 0 W to 2000 W.

FIGS. 6A and 6B show an example of result of experiments for comparingthe amount of leakage of the heat transfer gas supplied to the spaceformed between the electrostatic chuck 25 and the focus ring 30 in thesecond embodiment. In FIGS. 6A and 6B, the vertical axis represents theamount of leakage (sccm) of He gas supplied as the heat transfer gas tothe space formed between the electrostatic chuck 25 and the focus ring30, and the horizontal axis represents an accumulated time (hr) of theplasma processing performed in the plasma processing period.

In FIG. 6A, graph 152 shows the amount of leakage of He gas in the caseof performing plasma processing without using the electrostaticattraction process for applying different voltages to the innerperipheral electrode plate 25 d-1 and the outer peripheral electrodeplate 25 d-2 in the cleaning period.

In FIG. 6B, graph 162 shows the amount of leakage of He gas in the caseof performing plasma processing by using the electrostatic attractionprocess for applying different voltages to the inner peripheralelectrode plate 25 d-1 and the outer peripheral electrode plate 25 d-2in the cleaning period.

As shown in FIG. 6A, the amount of leakage of He gas in each plasmaprocessing was increased by about 1 sccm in the case of not using theelectrostatic attraction process for applying different voltages to theinner peripheral electrode plate 25 d-1 and the outer peripheralelectrode plate 25 d-2 in the cleaning period.

On the other hand, the amount of leakage of He gas in each plasmaprocessing was increased by less than 1 sccm in the case of using theelectrostatic attraction process for applying different voltages to theinner peripheral electrode plate 25 d-1 and the outer peripheralelectrode plate 25 d-2 in the cleaning period. In other words, in thecase of using the electrostatic attraction process for applyingdifferent voltages to the inner peripheral electrode plate 25 d-1 andthe outer peripheral electrode plate 25 d-2 in the cleaning period, itis possible to suppress the increase in the amount of leakage of theheat transfer gas supplied to the space formed between the focus ring 30and the electrostatic chuck 25.

In the first and the second embodiment, there has been described aperiod in which the wafer W is loaded into the processing chamber 10, aperiod in which the wafer W is unloaded from the processing chamber 10,and a cleaning period as a period other than the plasma processingperiod. However, such a period is not limited thereto. For example, thecontrol unit 43 may control such that different voltages are applied tothe inner peripheral electrode plate 25 d-1 and the outer peripheralelectrode plate 25 d-2 to generate a potential difference between theinner peripheral electrode plate 25 d-1 and the outer peripheralelectrode plate 25 d-2 in a period other than the plasma processingperiod, i.e., a period in which the operation of the substrateprocessing apparatus (plasma processing apparatus) is stopped.Accordingly, in the period in which the operation of the substrateprocessing apparatus is stopped, the misalignment between theelectrostatic chuck 25 and the focus ring 30 is avoided and theairtightness of the space formed between the electrostatic chuck 25 andthe focus ring 30 is ensured. As a result, in the plasma processingperiod, it is possible to suppress the increase in the amount of leakageof the heat transfer gas supplied to the space formed between the focusring 30 and the electrostatic chuck 25.

Further, for the sake of convenience, in the first and the secondembodiment, the electrodes are arranged at the inner peripheral side andthe outer peripheral side of the focus ring 30. However, the arrangementof a plurality of electrodes is not limited thereto. For example, aplurality of electrodes may be arranged at positions serving aselectrostatic chucks. In this case, the control unit 43 may control suchthat a voltage of a predetermined polarity is applied to some of theplurality of electrodes and a voltage of the opposite polarity isapplied to the other electrodes.

Hereinafter, an arrangement example of a plurality of electrodes will bedescribed. FIG. 7 explains a first arrangement example of a plurality ofelectrodes. As shown in FIG. 7, a plurality of electrodes may beconcentrically arranged at a region in the electrostatic chuck 25 whichcorresponds to the focus ring 30.

FIGS. 8A and 8B explain a second arrangement example of a plurality ofelectrodes. As shown in FIGS. 8A and 8B, a plurality of electrodes maybe arranged in semi circles at a region in the electrostatic chuck 25which corresponds to the focus ring 30.

FIG. 9 explains a third arrangement example of a plurality ofelectrodes. As shown in FIG. 9, a plurality of electrodes may bealternately arranged at a region in the electrostatic chuck 25 whichcorresponds to the focus ring 30.

While the disclosure has been shown and described with respect to theembodiments, it will be understood by those skilled in the art thatvarious changes and modifications may be made without departing from thescope of the disclosure as defined in the following claims.

What is claimed is:
 1. A substrate processing apparatus comprising: aprocessing chamber configured to provide a processing space; a substratemounting part configured to electrostatically attract a substrate; afocus ring; a focus ring mounting part configured to electrostaticallyattract the focus ring, the focus ring mounting part surrounding thesubstrate mounting part and including a plurality of electrodes; asupply unit configured to supply a heat transfer medium to a spaceformed between the focus ring and the focus ring mounting part; and acontrol unit configured to supply the heat transfer medium by the supplyunit to the space for a plasma processing period for which a plasma isgenerated in the processing chamber and to generate a potentialdifference among the plurality of electrodes to attract the focus ringfor a period other than the plasma processing period, wherein the focusring includes a bottom surface extending continuously from an outerperiphery of the bottom surface to an inner periphery of the bottomsurface, and wherein the plurality of electrodes are disposed below thebottom surface of the focus ring such that each electrode from theplurality of electrodes is partially overlapped or entirely overlappedby the bottom surface of the focus ring from a top view perspective ofthe focus ring.
 2. The substrate processing apparatus of claim 1,further comprising an electrostatic chuck including the substratemounting part and the focus ring mounting part, wherein the substratemounting part comprises a substrate attracting electrode for attractingthe substrate on a central portion of the electrostatic chuck, whereinthe substrate attracting electrode and the plurality of electrodes areeach positioned between a pair of dielectric films.
 3. The substrateprocessing apparatus of claim 1, wherein, during the period other thanthe plasma processing period, the control unit is configured to attractthe focus ring in a state where the heat transfer medium is not suppliedto the space.
 4. The substrate processing apparatus of claim 1, whereinthe control unit is configured to generate the potential differenceamong the plurality of electrodes by applying voltages having differentpolarities to the plurality of electrodes.
 5. The substrate processingapparatus of claim 1, wherein the plasma processing period includes aperiod for plasma processing the substrate and a cleaning period forcleaning the processing chamber after the period for plasma processingthe substrate.
 6. The substrate processing apparatus of claim 1, whereinthe substrate processing apparatus further includes a center electrodepositioned radially inside of the plurality of electrodes, and whereinthe control unit is configured to control application of voltages to thecenter electrode and the plurality of electrodes such that: a voltage isapplied to the center electrode during the plasma processing period; avoltage is applied to at least one of the plurality of electrodes duringthe plasma processing period; and no voltage is applied to the centerelectrode during the period other than the plasma processing period, andat least two different non-zero voltages are applied to the plurality ofelectrodes during the period other than the plasma processing period. 7.The substrate processing apparatus of claim 6, wherein the control unitis configured to control application of voltages of different polaritiesto the plurality of electrodes during the period other than the plasmaprocessing period.
 8. The substrate processing apparatus of claim 6,wherein the control unit is configured to control application of a samevoltage to each of the plurality of electrodes during the plasmaprocessing period.
 9. An electrostatic chucking method using a substrateprocessing apparatus including: a processing chamber configured toprovide a processing space; a substrate mounting part configured toelectrostatically attract a substrate; a focus ring; a focus ringmounting part configured to electrostatically attract the focus ring,the focus ring mounting part surrounding the substrate mounting part andincluding a plurality of electrodes; a supply unit configured to supplya heat transfer medium to a space formed between the focus ring and thefocus ring mounting part; and a control unit, the method comprising:supplying the heat transfer medium by the supply unit to the space for aplasma processing period for which a plasma is generated in theprocessing chamber; and generating a potential difference among theplurality of electrodes to attract the focus ring for a period otherthan the plasma processing period, wherein the focus ring includes abottom surface extending continuously from an outer periphery of thebottom surface to an inner periphery of the bottom surface, and whereinthe plurality of electrodes are disposed below the bottom surface of thefocus ring such that each electrode from the plurality of electrodes ispartially overlapped or entirely overlapped by the bottom surface of thefocus ring from a top view perspective of the focus ring.
 10. Theelectrostatic chucking method of claim 9, wherein the substrateprocessing apparatus further comprises an electrostatic chuck includingthe substrate mounting part and the focus ring mounting part, whereinthe substrate mounting part comprises a substrate attracting electrodefor attracting the substrate on a central portion of the electrostaticchuck, wherein the substrate attracting electrode and the plurality ofelectrodes are each positioned between a pair of dielectric films.
 11. Aplasma processing method using a substrate processing apparatusincluding: a processing chamber configured to provide a processingspace; a substrate mounting part configured to electrostatically attracta substrate; a focus ring; a focus ring mounting part configured toelectrostatically attract the focus ring, the focus ring mounting partsurrounding the substrate mounting part and including a plurality ofelectrodes; a supply unit configured to supply a heat transfer medium toa space formed between the focus ring and the focus ring mounting part;and a control unit configured to supply the heat transfer medium by thesupply unit to the space for a plasma processing period for which aplasma is generated in the processing chamber and to generate apotential difference among the plurality of electrodes to attract thefocus ring for a period other than the plasma processing period, themethod comprising: loading the substrate into the processing chamber andmounting the substrate on the substrate mounting part; attracting thefocus ring by generating a potential difference among the plurality ofelectrodes; performing plasma processing on the substrate by generatingthe plasma in the processing chamber; supplying the heat transfer mediuminto the space during said performing plasma processing; and unloadingthe substrate from the processing chamber after the substrate isprocessed, wherein the focus ring includes a bottom surface extendingcontinuously from an outer periphery of the bottom surface to an innerperiphery of the bottom surface, and wherein the plurality of electrodesare disposed below the bottom surface of the focus ring such that eachelectrode from the plurality of electrodes is partially overlapped orentirely overlapped by the bottom surface of the focus ring from a topview perspective of the focus ring.
 12. The plasma processing method ofclaim 11, wherein the substrate processing apparatus further comprisesan electrostatic chuck including the substrate mounting part and thefocus ring mounting part, wherein the substrate mounting part comprisesa substrate attracting electrode for attracting the substrate on acentral portion of the electrostatic chuck, wherein the substrateattracting electrode and the plurality of electrodes are each positionedbetween a pair of dielectric films.
 13. The plasma processing method ofclaim 11, wherein said attracting is performed in a state where the heattransfer medium is not supplied to the space.
 14. The plasma processingmethod of claim 11, wherein said attracting is performed by applyingvoltages having different polarities to the plurality of electrodes. 15.The plasma processing method of claim 11, wherein voltages applied tothe plurality of electrodes during said performing plasma processing.16. The plasma processing method of claim 11, wherein the method furthercomprises, after said unloading, cleaning the processing chamber in astate where the heat transfer medium is supplied to the space.